Magnetic resonance imaging (MRI), or nuclear magnetic resonance imaging, is a noninvasive imaging technique that uses the interaction between radio frequency pulses, a strong magnetic field (modified with weak gradient fields applied across it to localize and encode or decode phases and frequencies) and body tissue to obtain projections, spectral signals, and images of planes or volumes from within a patient's body. Magnetic resonance imaging is particularly helpful in the imaging of soft tissues and may be used for the diagnosis of disease.
Once diagnosed, radiation therapy treatment can be performed by directing a source of ionizing radiation, a linear accelerator (linac) for example, to deliver a radiation beam to a patient as part of the treatment plan. The output of a linac can be monitored, in part, by beam diagnostics that measure properties of the beam during treatment.